1. Field of the Invention
The present invention relates generally to a method and apparatus for sealing tubes and more particularly to sealing high-pressure tubes such as used in heat exchangers.
2. Description of the Related Art
In high pressure applications, especially where high pressure steam is present, conventional methods of sealing high pressure tubes are not always practical. Welding is one method, but tight working spaces often make it difficult to weld an individual high-pressure tube.
Various plugs have been used successfully, each with their limitations. The particular problems encountered in the industry are very well articulated in prior U.S. Pat. No. 4,976,307 and U.S. Pat. No. 5,189,789, both of which are hereby incorporated by reference in their entirety. The present invention is an improvement over the embodiments disclosed in these prior patents. A method of repairing a leaking feed water heater is to seal both the inlet and outlet ends of the leaky U-shaped tube at the tube sheet. This is much faster and substantially more economical than replacing the entire tube or the tube bundle. It has been shown that a feed water heater may be operated economically even when up to 10% of the tubes within the feed water heater have been plugged. If more than 10% of the tubes are plugged, the efficiency of the system declines to a level at which it is more economical to replace or repair the U-shaped tube bundles. Even when more than 10% have been plugged, the removal of the feed water heater from service and subsequent repair or replacement may be planned in advance and executed in an economical, orderly, non-crisis manner.
The plug described in U.S. Pat. No. 5,189,789 has several limitations. This plug must be cooled at the job site to a temperature below −20° to 30° C. using a mixture of alcohol and dry ice. The plug must then be shaped or formed using a jig or tool, also at the job site. It is then inserted into the tube and allowed to return to room temperature, at which time it restores to its original shape, sealing the tube. Creating the temperature required to form the plug at the job site not only uses volatile chemicals that can be dangerous to handle, precise forming of the plug is very difficult and any deviation from the required shape may result in a weak plug that will fail under pressure.
What is needed is a plug that can be completely manufactured and formed in a factory then packed, shipped and ready to install right off the shelf a method of manufacturing the plug and a method of installing the plug at the job site using readily available tools.